1. Field of the Invention
The present invention relates generally to optical scanners and, more particularly to a method for bi-directional flatbed scanning and automatic document feed.
2. Background Art
Optical scanning and copying devices employ a method wherein data representative of a scanned object is produced by projecting an image of the scanned object onto an optical sensor. The optical scanning device may include scanner optics which may reduce the size of a projected image. The image of the scanned object is projected onto an optical sensor by linear increment by means of a moving scan line. The moving scan line is produced either by moving an image bearing media with respect to the scanner optical assembly or by moving the scanner optical assembly relative to an image bearing media. The optical sensor produce data representative of the intensity of the light projected thereon. These data may be digitized and stored on data storage media. Such stored data may be processed by a processing device to produce an image output or display.
Black and white or grayscale and some color optical scanning processes may require a single pass in order to acquire an image from which corresponding data is generated, processed and stored to produce an image of the object. Some color optical scanning processes require multiple passes in order to acquire multiple color component images from which corresponding data is generated and stored to produce a color image of the object. Typically data representative of red, green and blue component color images of the scanned object are produced and correlated for storage.
Various types of photosensor devices may be used in optical scanning devices. One such photosensor device is the charge coupled photosensor device or “CCD”. A CCD creates an electrical charge in response to exposure to light. The magnitude of the electrical charge created is dependent on the intensity and the duration of the light exposure.
In optical scanning devices CCD cells are aligned in linear arrays. Each cell has a portion of a scan line image projected thereon as the scan line sweeps across a scanned object. The charge in each of the cells is measured and discharged at a “sampling interval”. The direction parallel to the scan line movement relative to the object is the “scan direction”. A scanner linear photosensor array includes a set of cells aligned in a “cross linear array”, i.e. in a direction perpendicular to the scan direction. Each cell is defined by a width and a length, the width measured in the scan direction and the length measured in the cross linear direction. Scanners typically operate at a scanline sweep equal to one cell width per CCD sampling interval. At any time during a scanning operation, each cell in the CCD array includes an area that corresponds to an area of the object which is being imaged. This area of the CCD array is referred to herein as a “cross linear sampling”. The corresponding area of the scanned object is referred to herein as an “object linear segment”.
In flatbed optical scanning devices and copiers of the prior art, image bearing media is placed on a transparent platen and the carriage assembly scans the image from the top of the page to the bottom of the page while the image remains stationary on the transparent platen. When the top to bottom scan is complete, the carriage assembly returns to a top of the page position ready for the next top to bottom scan. In a black and white or one pass color scanning device, two traverses of the page length are required to scan a single image. In a multiple or three pass color scanning device, six traverses of the page length are required to scan a single image.
In a flatbed optical scanning device including an automatic document feed (ADF), image bearing media will be fed in repeated sequence for positioning on the flatbed for scanning and then on to an output document tray or document receiver. The carriage assembly repeatedly cycles from top to bottom and bottom to top scanning media in repeated sequence from the top of the page to the bottom of the page until such time as the ADF no longer contains media for feeding. The process repeats until the last image is scanned and then the carriage assembly returns to a top of the page position ready for the next scan job.
Processor operable image processing software processes digital data representative of the scanned image or images for storage, transmission, display, printing or other output.
It may be desirable to reduce the number of scanner carriage movement sequences by substantially 50 percent. It may be desirable to reduce scanning time by substantially 50 percent. It may also be desirable to increase the reliability of a scanning device by reducing total operation time for any given multi-page scanning task. It may also be desirable to improve long term scan and print quality by reducing the total mechanical stress over the life of the scanning device caused by vibration by reducing total operation time.